The invention concerns a process for thermal treatment of liquid or semi-liquid hydrocarbon charges, in order to convert them to lighter gaseous or liquid products. The process makes use of a reactor with an ultra-short residence time providing for a high and very quick thermal transfer between a heat carrier and said hydrocarbons.
A process for the steam-cracking of oil fractions is already known (B. P. Ennis, H. B. Boyd, R. Orris--Chemtech, November 1975, p. 693), but this process remains limited to:
the treatment of light hydrocarbon charges, in order to avoid substantially high coke deposits on the reactor walls,
the treatment at relatively moderate temperature since the mechanical strength of the tubes requires a temperature not in excess of 900.degree. C.
Another technique of thermal cracking under pressure in the presence of hydrogen (French Pat. No. 2,164,450) makes it possible to direct the reactions to a production of light olefins preferentially to that of the corresponding saturated hydrocarbons. The selectivity to olefins results from the use of moderate temperatures (625.degree. to 900.degree. C.) and of a short residence time (0.01 to 0.1 s).
However, this type of process, as a result of the practical limitations concerning the temperature and the residence time, cannot be applied to heavy fractions containing aromatic hydrocarbons.
For the treatment of heavy hydrocarbon charges, the heat transfer through tubes being no longer possible, the heat supply may be effected by intimate contact between solid particles brought to high temperature and the charge sprayed in a fluidized bed (U.S. Pat. No. 3,855,070).
These techniques have the disadvantages of favouring the formation of tars and the agglomeration of the particles to the prejudice of the reaction yield.